I realise of course that this is somewhat late, since it is now four years since the UK passed legislation to permit the marriage of same-sex couples. However, the debate is still very much live in the church, including in the Church of England, while issues around the interaction between equalities legislation and the protection of fundamental freedoms continue to come before the courts. It is also still a live issue in other countries, especially Australia where a postal ballot on the subject is currently taking place.

I have not always been opposed to same-sex marriage. Like many of my generation I was brought up on a diet of the sexual revolution to believe that there was nothing wrong with homosexual relationships, and my church never mentioned it. It is only as I have got older and understood more of the ways of the world and God’s ways that I have come to regard human relationships in a new light. So one thing at least can be said for the view presented here: it isn’t the product of ingrained prejudice or instinctual distaste, but one arrived at through a long process of reasoned consideration of the facts of the matter (or at least as they have appeared to me).

As a Christian, my views on the issue are informed by two sources: general revelation (or the revelation to reason) which is truth from God as it is discerned by the human intellect reflecting on the order and course of nature; and special revelation (or historical revelation) which is truth contained in the works and words of the living God as they have been recorded authoritatively in holy scripture. From these I get two broad types of argument: biblical arguments and rational moral arguments. Both of these will play a role in the account presented here.

On the most basic level my understanding of marriage is that it is part of the moral order that God has laid down for his rational creatures, for human beings made in his image. Other aspects of this order include respect for human life, for truth, for property, for one’s parents, and for God. Although its most important tenets are set down in the Ten Commandments as revealed by God to Moses, it is knowable by all people since it is ‘written on their hearts’ (Romans 2:15).

Marriage is the aspect of the moral law which governs the relations between the sexes and, consequently, the raising of children.

On its most basic level (functionally speaking, I mean – marriage as a lived experience is obviously far more than this) marriage is the aspect of the moral order which governs the natural function of reproduction and those things which attend it, such as sexual intimacy and the nurture of offspring. Human beings, like many other creatures in the natural world, reproduce sexually through the female becoming pregnant through fertilisation by the male. On a purely natural level this is the basic reason why humanity, like other creatures which reproduce sexually, are divided into male and female – it is why there is man and woman rather than a single sexless humanity. It is also, on that same basic level, why there is sex: the sexual organs are part of the reproductive system of the human organism, and male and female sexual anatomy are complementary in a way which enables the male to fertilise the female and thus the female to give birth to their joint biological offspring. The reason the term sex is common to all these things is because they are all to do with this system of sexual reproduction.

The moral order for human beings, made in the image of God, is not the same as the natural order set down for other creatures which also reproduce sexually. Indeed, the natural world displays all kinds of sexual behaviour and approaches to the raising of offspring, from lifelong fidelity to promiscuous insemination, from those who care for their offspring into adulthood to those who abandon them immediately (and even eat a few). Then there are animals which live in colonies with a single queen and those which live in groups with a dominant male. If there’s one thing you can say from all this it’s that human beings should not take their moral code from the animal kingdom. Animals come with their own characteristic modes of sexual relations and reproduction, and they are not for imitation by human beings, who have been equipped by God with the capacity to know the moral law and the freedom to follow it for their own flourishing.

Animals are not the model for humans. But we must still contend with our animal nature. And part of that is that we too reproduce ourselves sexually through the union of male and female (and indeed we must if we are not to die out). In our case, of course, what is produced is not merely another animal, but another human being: a new unique human individual made in the image of God, with free will and the capacity to know God and grow in the capacity for reason and virtue. This new human being is, alongside other human beings, the most valuable thing in the universe, and so the moral rules aimed at protecting it and giving it the best chance to thrive are among the most important aspects of the moral law.

Marriage is the centrepiece of this moral law governing the relations between the sexes and thus sexual behaviour and the creation of offspring. Each new human being is the biological offspring of two other human beings, a male and a female, and resembles them both in his or her own unique character and constitution. To preserve this sacred bond between a human being and those who created him and are thus responsible for him the moral law requires that those who created him must remain committed to one another and to him and form a home environment suited to his successful nurture. Since sexual activity between a man and a woman is precisely what naturally produces offspring (and even in this age of contraception still does so in unintended fashion, as the persistently high abortion rate attests) the sexual activity itself also needs to be confined to relationships of commitment suited to the raising of children. These relationships of commitment are marriage.

This picture, however, is still incomplete. For if marriage was just about producing and caring for children then a number of things would not make sense about it. Such as why infertile couples or those whose children have left home should be morally required to remain married when they have no children or potential children to be concerned about. Or why same-sex couples (and groups of more than two) should not be permitted to marry, especially if they plan to adopt children.

Before addressing these issues, let us pause to consider what the Bible says.

The Bible presents a consistent picture of marriage as being between a man and a woman. Genesis 1:27-8 speaks of God creating humankind male and female in his own image so as to ‘be fruitful and multiply’, and Genesis 2:23-4 tells of the man leaving his father and mother and becoming one flesh with his wife. Jesus quoted these passages to underpin his prohibition on divorce (Matthew 19:4-6, Mark 10:6-9), and Paul cited them too, not only to repeat the standard teaching on marriage but also to add to it a mystical dimension as a picture of the relationship between Christ and the church (Ephesians 5:28-33). The biblical vision of marriage, then, is always and essentially gendered, involving the union of male and female.

Scripture is also always negative about same-sex sexual activity. Same-sex sexual activity is explicitly mentioned three times in the New Testament, in Romans 1:26-7, 1 Corinthians 6:9, and 1 Timothy 1:9-11. In each of these it is included as an example of sin or vice, and in the passage from Romans it is mentioned as a sin of particular depravity, linked with idolatry. Some argue that these references are only to certain forms of same-sex sex, such as exploitative ones, and certainly not to sex within a modern, loving, committed same-sex union, which were allegedly unknown in the ancient world.

However, a great many scholars, including those committed to affirming same-sex relationships, are under no doubt that all same-sex sex, in any context, loving or not, is included in these sins (or rather all male same-sex sex is, and female also very likely in Romans 1:26) – scholars such as Bernadette Brooten, Louis Crompton, Luke Timothy Johnson, Diarmaid MacCulloch, Martti Nissinen, Pim Pronk, William Schoedel, Dan O. Via and Walter Wink. There is also a lot of evidence that loving same-sex relationships were widely known about in the ancient world (in Plato’s Symposium for example), at least in certain eras, and thus aren’t an exclusively modern phenomenon.

The view of most of the above scholars is that, as MacCulloch tersely puts it, ‘in this, as in much else, the Bible is simply wrong’. Yet it is worth noting that this is the only one of the sins or vices listed in the various places in the New Testament that anyone has any wish to strike off. This is the only one that God (assuming he had any involvement in producing the Bible) failed to prevent being erroneously included. It all seems pretty convenient that this happens to coincide with lifestyles that many of these scholars themselves wish to lead, and in any event that it so agreeably harmonises with the spirit of the age. Is it not much more likely that the disapproval of same-sex sex, like the other sins and vices included, accurately describes the mind of God on these matters?

But let us return to our justification of marriage as part of the moral order for humankind. The needs of children had seemed to get us so far, but then we had been left with questions about why marriage was also for the childless and why it excluded same-sex couples (as well as larger groups).

The reason for both these features of marriage is the same, and it is that given in Genesis 2:23-4: because of the design of the human being as male and female with complementary anatomy through which a couple becomes one flesh. This is the design which God has given to human beings, and if we have any respect for God and his purposes in creation then we are bound to respect this design in the forms of relationship which we are permitted to sanction under the moral law. Infertile couples may participate in this design and form of marriage, albeit without the usual natural fruit. But other combinations – same-sex couples and larger groups – do not respect the design and so are disallowed.

A person might object that all this is somewhat abstract, and that if a same-sex relationship does no harm and benefits the couple then why should we hold to such abstract principles instead of going with what brings about most good? One response to this is to point out that all moral principles are on one level abstract ideas, and that the divine design of the human being would seem a somewhat important foundation for our ethical concepts.

But there is more we can say here. For we can flesh out the claim that same-sex sexual relationships are contrary to God’s design by highlighting the various risks and harms which research has shown disproportionately accompany same-sex relationships and gay culture. Some dispute the relevance of this, arguing that statistical patterns are just that and don’t imply anything about particular relationships, which may involve none of the stated problems. Nonetheless, statistical patterns of risks and harms are important facts which tell us something about the overall character of a thing, even if not about individual instances. Thus it is surely at least worth being aware that same-sex marriages have been shown to have very high rates of non-exclusivity (around 50% are open arrangements) and that such non-exclusivity even appears to be important for their long-term sustainability. Or that some of the favoured sexual practices of gay men in particular are associated with very high rates of venereal disease. Or that people who identify as gay suffer from considerably higher rates of depression and other mental illnesses, including in contexts where same-sex relationships are widely accepted. Or that adoption by same-sex couples intrinsically deprives the children involved of having either a mother or a father, while popular reproductive methods for same-sex couples (though not exclusive to them of course) such as surrogacy and sperm donation also deprive children of having a relationship with one of their two biological parents.

Such observations do appear to tell us something significant about the disordered nature of same-sex sexual relationships. But when push comes to shove they are really only illustrative of the wider point, that God has designed human beings as male and female for mutual attraction, and ultimately to become one flesh in marriage – for the two halves of the human race to come together in loving commitment, and in that way to propagate the human race. That is the pattern laid down at the beginning under the moral law by the Creator of humankind, and, Christian or not, we are not at liberty to set it aside.

That is the reason, ultimately, that I cannot support same-sex marriage. Of course I am also deeply concerned about further developments in the ever-widening LGBT agenda, such as the promotion of transgenderism, polyamory and the suppression of freedom of speech, conscience and religion. But same-sex marriage is also an issue in its own right, and it is I believe the solemn duty of all Christians everywhere to oppose it, and to stand their ground against the coming storm.